1. Field of the Invention
The invention relates to the use of compressors and compressed gas in fuel cell systems.
2. Background Art
Fuel cell systems produce electrical energy by combining fuel and an oxidant in a fuel cell stack. In one form of fuel cell system, the fuel is hydrogen and the oxidant is oxygen, which may be mixed with other gases as in air. The oxidant is typically gaseous and is often delivered to the fuel cell stack as a compressed flow.
Typically, fuel cell stacks operate more efficiently under certain operating conditions, including fuel cell stack temperature. In particular, it is desirable for the fuel cell stack to operate at or above a particular temperature, which may be above ambient temperature. Therefore, there is a need to heat the fuel cell stack at various times such as, for example, during startup.
Different types of compressors may be used to provide oxidant to the fuel cell stack. For example, non-positive displacement compressors are sometimes used for a variety of reasons such as size, weight, efficiency, noise, vibration, and harshness characteristics. However, non-positive displacement compressors may operate in an undesirable condition known as surge. Surge occurs when the compressor is operated at low flow rates in combination with a high ratio of output pressure to input pressure. Under these conditions, surge may result in vibrations which can lead to poor operation, malfunction system damage, and the like. In fuel cell systems that use ambient air to provide the oxidant, variations in air density and pressure can affect compressor performance. This is particularly true at higher elevations, where the onset of surge is more likely.
Fuel cell stacks are typically placed in a housing. Unwanted gasses may accumulate in the housing, requiring some mechanisms to vent or purge the unwanted gasses.
Fuel cell systems are often part of a larger system such as, for example, an automotive vehicle. These larger systems often require various environmental modification systems that could benefit from synergistic operation with the fuel cell system.
Accordingly, a need exists for improved fuel cell system operation which addresses some or all of the above issues without unduly affecting cost, complexity, performance, and the like.